1. Technical Field
Example embodiments of the present invention relate in general to the field of an apparatus for non-contact sample analysis, and more particularly, to an apparatus for non-contact sample analysis using terahertz waves.
2. Related Art
Recently, with increasing interest and demand for flexible products in displays of a mobile phone, a television, a touch panel, a solar cell and an electronic newspaper, a high performance electronic device product is needed. The high performance electronic device needs to have electrical resistance at a predetermined level or less while maintaining uniformity of resistance, and thus the device has to be subjected to a resistance measurement.
Currently, as a typical example of a method for measuring electrical resistance of electronic devices, a sheet resistance measurement method using a four-point probe is used in which four probes come in contact with a sample to measure its own sheet resistance, a first probe and a fourth probe are supplied with a constant voltage and a current flowing between a second probe and a third probe is measured, or the second probe and the third probe are supplied with a constant current and a voltage between the first probe and the fourth probe is measured, so that resistance can be calculated through Ohm's law. However, the four-point probe measurement method has a constraint in which a sample is damaged by the four probes in contact with the sample. In particular, when a measurement area to perform a resistance measurement on a large-scale sample is increased, a damaged area of the sample is also increased, and thus the measurement accuracy gradually is lowered due to the damaged area. In addition, since a sheet resistance measured at an edge of a sample shows a great deviation, the above method has difficulty in measuring a resistance of a large-scale sample.
To overcome the constraints with contact-type resistance measurement, methods and apparatuses for non-contact type resistance measurement using an electric field generated from electromagnetic waves have been suggested. For example, Korean Unexamined Patent Application Publication No. 10-2004-0106107 discloses a non-contact sheet resistance measuring instrument, and in particular, relates to a sheet resistance measuring instrument for measuring a resistance component of a sheet, such as a semiconductor wafer or lens, in which an object to be measured is located parallel to a direction of an electric field of electromagnetic waves generated by an electromagnetic wave transmitter, and an electromagnetic wave receiver detects electric field absorption of the object to be measured so that a resistance value can be measured in a non-contact manner.
In addition, Japanese Unexamined Patent Application Publication No. 2003-227855 discloses a method and an apparatus for measuring a sheet resistance, and in particular, relates to a method of measuring a sheet resistance of one of a metal, a super conductor, and a semiconductor, in which an object to be measured is mounted on a substrate holder to be parallel to a control conductor having a sheet resistance, a dielectric load is fixed while spaced a predetermined distance from the object to be measured, and high-frequency electromagnetic waves are applied to the dielectric load to generate an electromagnetic field to resonate the conductor and the object to be measured so that a sheet resistance of the object to be measured can be measured from the resonance.
However, the above-described apparatus and method for sheet resistance measurement using an electric field has a low measurement accuracy compared to the contact-type apparatus and method, and has difficulty in recognizing a position of a transparent electrode and an electronic device in which damage has occurred. Accordingly, there is difficulty conducting a performance evaluation of a sheet resistance measurement together with a reliability evaluation of a resistance uniformity measurement.
Meanwhile, terahertz waves refer to electromagnetic waves ranging between microwaves and optical waves that have both a transmission property of electric waves and an absorptiveness property of light so that terahertz waves can pass through various types of materials (plastic, ceramic, paper, rubber and clothes), and are entirely reflected by a metal. Accordingly, terahertz waves, when radiated onto an electronic device, pass through a substrate formed of a highly polymerized compound that supports an electrode and are reflected from an electrode formed of a metal. Accordingly, at a damaged portion of the electrode on the substrate, intensity of the reflected waves is reduced or intensity of transmitted terahertz waves is increased. Accordingly, there is a need to develop an apparatus and a method for effectively measuring sheet resistance of an electronic device in a non-contact manner by using the unique characteristics of terahertz waves.